Device and method for the recovery of waste heat of an internal combustion engine

ABSTRACT

The invention relates to a device and a method for the recovery of waste heat from an internal combustion engine ( 2 ). A feed pump ( 6 ), a heat exchanger ( 8 ), an expansion engine ( 10 ) and a capacitor ( 12 ) are arranged in a circuit ( 4 ) containing a circulating working medium. A steam accumulator ( 40 ) for storing the vaporous working medium is also arranged in the circuit ( 4 ).

BACKGROUND OF THE INVENTION

The German patent publication DE 10 2006 057 247 A1 discloses a charging unit, which serves to recover waste heat from an internal combustion engine. At least one heat exchanger of a circuit of a working medium is housed in the exhaust system of the internal combustion engine. In addition, a turbine part and a conveyor assembly are disposed in the circuit. A compressor part disposed in the intake system of the internal combustion engine is driven via the turbine part.

SUMMARY OF THE INVENTION

The device according to the invention for the recovery of waste heat of an internal combustion engine and the associated inventive method having the features of the independent claims have the advantage that steam, which is not required at a certain point in time, is stored and is passed on only when required or when a load demand is placed on the expansion engine.

When a momentary change in load on the internal combustion engine occurs, as is the case during deceleration of a motor vehicle, the heat given off by the exhaust gas system cannot be completely fed back to the drive train of the vehicle because a load demand does not occur at this moment. The heat energy given off by the exhaust gas system would be lost if a suitable storage system were not available. The heat energy can be stored by means of the steam accumulator and be used again at a later point in time.

Another example of a momentary change in load on the internal combustion engine is a passing maneuver of a vehicle after a previous deceleration. In this instance, the internal combustion engine momentarily requires a very high level of energy, which can be extracted from the steam accumulator.

The heat energy of the exhaust gases and the exhaust gas recirculation is always provided to the expansion engine in a temporally delayed manner due to the thermal inertias of the at least one heat exchanger and the thermal inertia of the heat transfer. An advantage of the invention is that heat energy can be stored by the steam accumulator and again be made available when a momentary load demand occurs.

A further advantage results from the arrangement of the steam accumulator in a line of the circuit between heat exchanger and expansion engine because the steam accumulator is disposed between steam generator and steam consumer and therefore no further losses occur over long conveyance paths.

By means of an arrangement, in which the steam accumulator is directly connected to the heat exchanger via a branch line, the advantage ensues that a common insulation and a common installation space can be used as a result of the spatial proximity between heat exchanger and steam accumulator.

A connection between expansion engine and steam accumulator via a branch line is advantageous because in the case of a momentary load demand across the expansion engine, steam is immediately available for operating said expansion engine and no loss of time occurs over long conveyance paths.

A further advantageous arrangement of the steam accumulator results from said steam accumulator being connected via a branch line to a line between the heat exchanger and the expansion engine. This is due to the fact that the steam generated by the heat exchanger does not inevitably flow through said steam accumulator on the way to the expansion engine.

A controllable valve proves to be particularly advantageous in one of the previously mentioned branch lines because the accomodation and release of steam can be deliberately controlled via the controllable valve, and therefore an intervention can be made into the control of the thermodynamic circuit through which the working medium flows. By means of a targeted opening and closing of the valve, pressure fluctuations in the heat exchanger and the connecting lines can be reduced. In addition, the evaporation temperature can be influenced by the accommodation and release of heat from the circuit.

The disposal of the steam accumulator in a bypass connection parallel to the expansion engine is advantageous because steam from the steam accumulator can be led by the expansion engine via the bypass connection. In so doing, heat energy can also be released to an attached cooling circuit via the condenser.

A disposal of the steam accumulator in a bypass connection is particularly advantageous if said steam accumulator is connected to the bypass connection via a multi-port-valve. The advantage results from the fact that such a disposal is a reliable option for controlling the accommodation and release of steam in all possible directions. The steam can furthermore be led directly from the heat exchanger past the steam accumulator to the condenser by means of the multi-port-valve. This is advantageous if the steam accumulator cannot accommodate any steam or if the steam is not of sufficient quality due to the superheating being too low.

A particularly cost effective solution for a steam accumulator in a bypass connection in parallel with the expansion engine is the use of a controllable valve on the side facing the heat exchanger and the use of an overflow valve on the opposite side. By means of the controllable valve, the steam can be accommodated and released by the steam accumulator in a targeted manner, while the overflow valve prevents too high of a pressure from occurring in said steam accumulator.

The reduction of pressure pulsations and pressure oscillations by steam being released from the steam accumulator and/or steam being accommodated by said accumulator is advantageous because no costs arise for additional components to suppress pressure oscillations.

As a result of steam being accommodated and released via the steam accumulator by means of the controllable valve for regulating the evaporation pressure, components as, e.g., additional storage volumes for the working medium in the vaporous or liquid state can be omitted.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are depicted in the drawings and described in detail in the following description. In the drawings:

FIG. 1 shows a device for the recovery of waste heat in a schematic depiction according to a first exemplary embodiment;

FIG. 2 shows a device for the recovery of waste heat in a schematic depiction according to a second exemplary embodiment;

FIG. 3 shows a device for the recovery of waste heat in a schematic depiction according to a third exemplary embodiment; and

FIG. 4 shows a device for the recovery of waste heat in a schematic depiction according to a fourth exemplary embodiment.

DETAILED DESCRIPTION

FIGS. 1 to 4 show a device for the recovery of waste heat from an internal combustion engine 2 comprising a circuit 4 containing a circulating working medium. At least one heat exchanger 8, an expansion engine 10, a condenser 12 and a feed pump 6 are disposed in the circuit 4. A steam accumulator 40 for storing a vaporous working medium is furthermore provided in the circuit 4, as is later described in detail in the description of the individual exemplary embodiments.

The internal combustion engine 2 can particularly be embodied as an air-compressed, self-ignited internal combustion engine 2 or as a mixture-compressed, spark-ignited internal combustion engine 2. The device for waste heat recovery is specially suited to applications in motor vehicles. Said inventive device for waste heat recovery is, however, also suited to other applications.

The internal combustion engine 2 burns fuel in order to produce mechanical energy. The exhaust gases resulting in the process are discharged via an exhaust gas system, in which an exhaust gas catalyst can be disposed. A duct section 22 of the exhaust gas system is led through the heat exchanger 8. Heat from the exhaust gases or the exhaust gas recirculation is emitted to the working medium provided in the heat exchanger 8 via the duct section 22; thus enabling the working medium in the heat exchanger 8 to be evaporated and superheated.

The heat exchanger 8 of the circuit 4 is connected to the expansion engine 10 via a line 26. The expansion engine 10 can be embodied as a turbine or a reciprocating engine. The evaporated working medium flows to the expansion engine 10 via the line 26 and drives the same. The expansion engine 10 has an output shaft, via which said expansion engine 10 is connected to a load. In so doing, mechanical energy can, for example, be transferred to a drive train or serve to drive an electrical generator, a pump or the like. After flowing through said expansion engine 10, the working medium is led to the condenser 12 via a line 28. The working medium expanded via the expansion engine 10 is cooled in the condenser 12. The condenser 12 can be connected to a cooling circuit 20. Said cooling circuit 20 can relate to a cooling circuit of the internal combustion engine 2. The working medium liquefied in the condenser 12 is transported via the line 29 from a feed pump 6 into the line 24.

A pressure control valve 27 is situated in the line 24 which serves to control pressure in the feed to the heat exchanger 8. With the aid of the predefined pressure in the feed to the heat exchanger 8, the evaporation temperature of the working medium can be controlled. In addition, a bypass connection 31, in which a pressure relief 30 valve is situated, can be provided in parallel with the feed pump 6. The maximally admissible pressure of the working medium between feed pump 6 and heat exchanger 8 can be set by means of the pressure relief valve 30.

The line 24 leads directly into the heat exchanger 8, in which the working medium is evaporated and superheated. The evaporated working medium arrives again at the expansion engine 10 via the line 26 and the working medium again flows through the circuit 4. A flow direction of the working medium through the circuit 4 is determined by the feed pump 6 and the expansion engine 10. Heat energy, which can be released in the form of mechanical energy to the load 11, can therefore be continuously extracted from the exhaust gases and the exhaust gas recirculation of the internal combustion engine 2 via the heat exchanger 8.

Water or another liquid, which corresponds to the thermodynamic requirements, can be used as the working medium. The working medium experiences thermodynamic changes in state when flowing through the circuit 4. In the liquid phase, said working medium is brought to the pressure level required for evaporation. The heat energy of the exhaust gas is subsequently given off to said working medium via the heat exchanger 8. In so doing, said working medium is isobarically evaporated and subsequently superheated. The steam is then adiabatically expanded in the expansion engine 10. In so doing, mechanical energy is obtained and transferred to the shaft 11. Said working medium is then cooled in the condenser 12 and supplied again to the feed pump 6.

In the exemplary embodiment in FIG. 1, the steam accumulator 40 is situated in the line 26 of the circuit 4 between heat exchanger 8 and expansion engine 10.

Steam delivered from the heat exchanger 8 can be accommodated in the steam accumulator 40 and be released again from said steam accumulator 40 when a load demand is placed on the expansion engine 10.

FIG. 2 shows a second exemplary embodiment in which the steam accumulator 40 is connected to the circuit 4 via a branch line 44. The branch line 44 opens out into the line 26 of the circuit 4 between heat exchanger 8 and expansion engine 10. A controllable valve 42, via which steam can be selectively released or accommodated, can be disposed in the branch line 44.

As a further embodiment, the branch line 44 can alternatively also be directly connected to the heat exchanger 8 or to the expansion engine 10; thus enabling a spatial proximity to the steam generator or steam consumer to occur. The two alternatives are indicated in FIG. 2 by the dashed line 44. In this case, controllable valves 42 can also be disposed in the branch line 44.

A third exemplary embodiment is depicted in FIG. 3. The steam accumulator 40 is situated in a bypass connection 14, which is connected in parallel to the expansion machine 10. The steam accumulator 40 is connected to the bypass connection 14 via a multi-port-valve. The multi-port-valve 46 has a plurality of switching options via which the steam can be accommodated or released by the steam accumulator 40 or led past said steam accumulator 40.

In order to accommodate steam, the multi-port-valve 46 can establish a connection between a line 13 of the bypass connection 14 which faces the heat exchanger 8 and the steam accumulator 40. In this position of the multi-port-valve 46, steam produced in the heat exchanger 8 flows via the line 26 and the line 13 into the steam accumulator 40.

In the event of a load demand being applied to the expansion engine 10, the multi-port-valve 46 can again establish a connection between the line 13 of the bypass connection 14 which faces the heat exchanger 8, and the steam accumulator 40. In this case, steam flows out of said steam accumulator 40 to the expansion engine 10 via the line 13 and the line 26.

In the event of no load demand being applied to the expansion machine 10, the multi-port-valve 46 can establish a connection between steam accumulator and a line 15 of the by pass connection 14 which faces the condenser 12. The steam flows to the condenser 12 via the line 15 and the line 28. The heated steam can give off heat via the condenser 12 to the cooling circuit of the internal combustion engine 2 or to another cooling circuit in the vehicle.

If the heated steam is to be led past the expansion engine 10 but not accommodated by the steam accumulator 40, the multi-port-valve 46 can establish a direct connection between the line 13 and the line 15 of the bypass connection 14. If no load demand is applied to the expansion machine 10 but heated steam is further produced in the heat exchanger 8, said heated steam can then be led by the expansion engine via the bypass connection 14.

FIG. 4 shows a fourth exemplary embodiment, in which the steam accumulator 40, as in FIG. 3, is disposed in the bypass connection 14. Said steam accumulator 40 is connected via a controllable valve 48 to the line 13 of the bypass connection. On the opposite side, said steam accumulator 40 has an overflow valve 50, via which said steam accumulator 40 is connected to the line 15 of the bypass connection 14.

The accommodation and the release of steam via line 13 can be controlled by means of the controllable valve 48. If more steam is produced by the heat exchanger 8 than is required by the expansion engine 10, said excess steam can be received by the steam accumulator 40 via the controllable valve 48. If the expansion engine momentarily requires steam or if said engine hat a particularly high load demand, steam from the steam accumulator 40 can arrive at said expansion engine 10 via the controllable valve 48, the line 13 and the line 26.

If a larger quantity of steam is accepted via the controllable valve 48 than the steam accumulator 40 can accommodate, said excess steam can be diverted via the overflow valve 50 when a predetermined pressure has been exceeded.

All depicted exemplary embodiments of the invention can accommodate steam delivered from the heat exchanger 8 in the steam accumulator 40 and release said steam when a load demand is placed on the expansion engine 10.

The steam accommodation in and steam extraction from the steam accumulator 40 can be actively controlled by the employment of a controllable valve 42, 46, 48 as that depicted in the embodiments in FIGS. 2-4. By opening the controllable valve 42, 46, 48, steam can be accommodated or released by the steam accumulator 40. If said controllable valve 42, 46, 48 is closed, steam is then led past the steam accumulator 40.

By actively controlling the steam accommodation and steam release of the steam accumulator 40 via the controllable valve 42, 46, 48, pressure oscillations or pressure pulsations in the circuit 4 can be reduced. By steam being released from the steam accumulator 40 and/or being accommodated by said steam accumulator 40, pressure oscillations in the heat exchanger 8 and in the connecting lines 24, 26 can be reduced.

By actively controlling the steam accommodation and steam release of the steam accumulator 40 via the controllable valve 42, 46, 48, the volume of the working medium in the circuit 4 can also be changed and thereby intervention can be made into the regulation of the evaporation pressure. 

1. A device for the recovery of waste heat from an internal combustion engine comprising a circuit in which a feed pump, at least one heat exchanger, an expansion engine and a condenser are arranged, wherein said circuit contains a circulating working medium, wherein a steam accumulator for storing the vaporous working medium is also arranged in the circuit.
 2. The device according to claim 1, wherein the steam accumulator is situated in a line of the circuit between heat exchanger and expansion engine.
 3. The device according to claim 1, wherein the steam accumulator is directly connected to the heat exchanger via a branch line.
 4. The device according to claim 1, wherein the steam accumulator is directly connected to the expansion engine via a branch line.
 5. The device according to claim 1, wherein the steam accumulator is connected to the line between the heat exchanger and the expansion engine via a branch line.
 6. The device according to claim 3, wherein a controllable valve is disposed in the branch line.
 7. The device according to claim 2, wherein the steam accumulator is situated in a bypass connection, which is connected in parallel with the expansion engine.
 8. The device according to claim 7, wherein the steam accumulator is connected to the bypass connection via a multi-port-valve, via which steam is accommodated or steam is released to lines to the expansion engine or to the condenser via lines.
 9. The device according to claim 7, wherein the steam accumulator has a controllable valve on the side facing the heat exchanger and an overflow valve on the opposite side.
 10. A method for the recovery of waste heat from an internal combustion engine for a device according to claim 1, wherein steam delivered from the heat exchanger is accommodated in the steam accumulator and is released from said steam accumulator when a load demand is placed on the expansion engine.
 11. The method according to claim 10, wherein pressure pulsations and pressure oscillations are reduced by steam being released from the steam accumulator and/or being accommodated by said steam accumulator.
 12. The method according to claim 10, wherein intervention is made into the regulation of the evaporation pressure by the accommodation and release of steam by the steam accumulator being actively controlled via a controllable valve. 